The present invention relates generally to corrosion reduction or mitigation, and in particular to the use of liquid applied coatings for substrate surfaces providing galvanic protection of metal structures imbedded within the substrate.
Corrosion of reinforcing steel in concrete is an insidious problem, affecting structures, highway bridge infrastructure, and building structures. Since the corrosion of steel in concrete progresses inside of the formed concrete slabs, the imbedded steel surface to be protected is not readily available for coating operations. Providing protection to the steel to significantly slow or stop the corrosion process would prevent further structural deterioration of the reinforced concrete system.
Other techniques have been used recently to offer protection of the steel reinforcing bars inside concrete structures. These include migrating corrosion inhibitors and cathodic protection systems. The chemical inhibitors promise quick and inexpensive protection, however, the corrosion processes can still continue in areas not sufficiently treated. These materials only slow the corrosion process and can still lead to structural damage of the concrete. The cathodic protection methods promise to stop the corrosion process by providing electrical current or sacrificial anodes.
The simplest impressed current methods require coating of the structure with a conductive paint and applying current by the use of an externally connected power supply. This system is costly to install, requires continuous power with associated costs, and must be periodically monitored and maintained for the life of the structure. Other impressed current systems on the market can be even more complicated.
The sacrificial cathodic protection method currently in use in industry requires the application of metallic zinc by arc or thermal spray equipment. This equipment is bulky, expensive, requires high skill to operate. This process also requires high voltage electricity to operate. This high voltage requirement is a great safety concern.
The existing cathodic protection systems on the market can be costly to install and require continuing maintenance to allow for proper protection. The impressed current systems can be very complex to install and must be adjusted during operation to optimize protection. Some galvanic systems require the use of costly arc spray equipment to apply the metallic zinc used for the protective current.
For the reasons stated above, and for other reasons stated below that will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for alternative methods and materials for reducing corrosion of imbedded metal structures.
Coating compositions and methods of their use are described herein for the reduction of corrosion in imbedded metal structures. The coatings are applied as liquids to an external surface of a substrate in which the metal structures are imbedded. The coatings are subsequently allowed to dry. The liquid applied coatings provide galvanic protection to the imbedded metal structures. Continued protection can be maintained with periodic reapplication of the coating compositions, as necessary, to maintain electrical continuity. Because the coatings may be applied using methods similar to standard paints, and because the coatings are applied to external surfaces of the substrates in which the metal structures are imbedded, the corresponding corrosion protection may be easily maintained.
For one embodiment, the invention provides a method of preventing corrosion of metal in concrete. The method includes surrounding a metallic member with concrete and applying a liquid coating to the concrete surface, the liquid coating having metallic particles which provide a protective current to the metallic member.
For another embodiment, the invention provides a method of slowing corrosion of metal structures imbedded in a substrate. The method includes applying a liquid coating to an external surface of the substrate. The liquid coating includes zinc and magnesium in a coating vehicle in an amount sufficient to remain conductive after application.
For yet another embodiment, the invention provides a liquid coating. The liquid coating includes a volume of zinc, a volume of magnesium and a volume of a coating vehicle. The liquid coating includes a sufficient volume of the zinc and magnesium to remain conductive after any solvents in the coating vehicle are driven off.
Further embodiments of the invention include apparatus and methods of varying scope.